U.S. Republican presidential candidate Donald Trump's campaign chairman, Paul Manafort, helped a Ukrainian political party with close ties to Russia secretly move at least $2.2 million to two major Washington lobbying firms, the Associated Press reported on Wednesday.

The AP, citing sources with direct knowledge of the effort, said the transfers were set up in ways to obscure the Ukrainian party's attempts to sway U.S. policies, using a non-profit organization to distance funds from Ukrainian politicians.

U.S. law requires American lobbyists to register and report in detail any ties to foreign political parties or leaders to the U.S. Justice Department.

The heads of both firms - Podesta Group Inc and Mercury LLC - told the AP they had concluded their work did not merit disclosure to the department, according to the report.

Representatives for Trump, Mercury and the Podesta Group could not be reached immediately for comment. The Podesta Group was founded in 1987 by Tony Podesta and his brother John, who now is campaign chairman for Democratic presidential candidate Hillary Clinton. John has not been with the firm for several years but Tony is its chairman.

The AP report comes less than three months before the Nov. 8 election and as polls show Trump slipping behind Democratic presidential nominee Hillary Clinton.

Trump's campaign on Wednesday announced a shake-up replacing Manafort as campaign manager after just two months. He will remain chairman and chief strategist.

The New York Times this week reported Manafort's name was found on secret ledgers showing cash payments designated to him of more than $12 million from a Ukrainian party with Russian ties. Manafort has denied any impropriety.

Ukrainian officials confirmed Manafort's name appeared on a ledger and that more than $12 million had been allocated as an expenditure but said the presence of his name did not mean he received the funds.

Clinton's campaign has said Manafort's associations are a troubling sign of ties between Trump's campaign team and pro-Kremlin elements in Ukraine.

According to the AP, in 2012 Manafort and associate Rick Gates worked on behalf of Ukraine's then-president, Viktor Yanukovych, and helped steer the efforts of European Centre for a Modern Ukraine, an advocacy group that once included members of Yanukovych's party.

The group paid at least $2.2 million to the Washington firms to push positions favorable to the party from 2012 until 2014, when Yanukovych was ousted and fled to Russia, AP said, citing sources. That work included efforts to counter a potential congressional resolution pressuring Yanukovych to release a political rival from prison, AP reported.

Gates told the AP his actions were lawful. He said he and Manafort had introduced the advocacy group to the firms and sometimes consulted with the firms on Ukrainian politics, the report said.